While the dynamics of model systems has been widely studied, the sizes of the systems has been limited. We present the dynamics for two large systems: a 9 degrees of freedom molecule and a 10000 state tier model. Classical non-linear resonance analysis and its quantum analog have been instrumental in providing insight into the pathways and rates of IVR processes in the overtone excitation of small molecules such as benzene and cyanoacetylene. It has been observed that the fourth overtone OH excitation of propargyl alcohol (PPA) is anomalously broad in comparison to the corresponding band of other small alcohols, possibly the result of rapid IVR out of the excited mode. An accurate model displayed no classical relaxation, but the quantum dynamics indicated an approximate degeneracy between the excited OH stretch and a combination band that can explain the observed broadening. To better understand the tier-to-tier relaxation process, an abstract model consisting of ten tiers of states was developed with the final tier representing the vibrational bath-states via a 50 state/cm$\sp{-1}$ state density. The survival dynamics showed irreversible relaxation out of the initial tier without the usual Poincare recursions. Interestingly, a calculation of the time-dependent spectrum showed the presence of only a few large features up to 720 fs which could not be attributed in a simple fashion to the dynamics of sub-models consisting the first n tiers. The early appearance and long persistence of a few broad bands implied the presence of "IVR resonances". In an attempt to elucidate these resonances, a imaginary damping function or optical potential was added to the model. An eigenvalue calculation on the resulting Hamiltonian did yield several long-lived resonances, and in fact, a spectrum calculated using only the first five resonances qualitatively reproduced the short pulse-length spectrum calculated from the original model. The "discovery" of these resonances is a step towards understanding and interpreting future pulselength dependent spectra in terms of the underlying tier structure of the systems studied.

FT-ICR studies of high mass $\rm (C\sb{>150})$ carbon clusters have brought insight to the controversial structures of carbon fullerenes. Laser vaporization followed by supersonic beam technique produced carbon clusters that directly injected into the bore tube of a 6 Tesla magnet. Mass spectra of the trapped cluster ions reveal the presence of only even-numbered clusters in the low mass regions, thus verifying the predominance of graphite closed shells. It is believed that the larger clusters also exist as aggregates loosely bound to each other on their surfaces and will readily disaggregate upon evaporation. When clusters of size C$\sb{300}$ or larger are fragmented by excimer laser, the products are mostly even-numbered ions resulting from C$\sb2$ loss which satisfy the retention of a fullerenes structure. In addition, there are distributions of multiply-charged high mass positive clusters detected as the photofragments undergo thermionic emission. This fragmentation experiment is currently used to compare the hypotheses of (1) giant fullerenes model where carbon condenses to form empty hollow cages of large radii, (2) aggregation of small clusters by van der Waals forces to form high mass clusters, and (3) "Russian-egg" model where high mass clusters exist as concentric closed shells.

A fundamental and long-standing question surrounds the mechanism of primary bond cleavage in azoalkanes: do the two C-N bonds break in a synchronous or a stepwise manner? When a vapor phase azoalkane absorbs near ultraviolet light, it dissociates into two alkyl radicals and nitrogen. Transient CARS spectroscopy was used here as a time-resolved probe of the photoproducts formed from azoalkanes excited at 355 nm. In a detailed reinvestigation, azomethane was found to dissociate in a stepwise process involving a methyldiazenyl radical intermediate. The diazenyl intermediate was formed in less than 1 ns and lived for 5.3 $\pm$ 1 ns before fragmenting into a methyl radical and nitrogen. Kinetic studies on azoisopropane (AIP) also gave evidence for stepwise photodissociation with a similar diazenyl lifetime. The first methyl radical formed in azomethane photodissociation was found to have 0 to 4 quanta of $\nu\sb2$ excitation, whereas the second methyl radical was predominantly vibrationally unexcited. The nascent rotational temperature of N$\sb2$ from azomethane was found to be 2500 K, and its vibrational distribution was confirmed to be 84% in v = 0 and 16% in v = 1. These results seem consistent with predictions based on the transition state structure computed for methyldiazenyl dissociation. Internal energy distributions were also measured for the nitrogen formed from 3-(methylazo)-3-methyl-butene (MAMB), which was previously shown to undergo stepwise dissociation through a methyldiazenyl intermediate. The rotational and vibrational energy distribution from MAMB were almost identical to those from azomethane, consistent with a common dissociation mechanism. AIP also gave similar nitrogen rotational and vibrational distributions, suggesting that the dissociative transition state of isopropyldiazenyl is similar to that of methyldiazenyl. In summary, direct kinetic measurements have demonstrated stepwise gas phase photodissociation in acyclic azoalkanes. Related measurements of product internal energy distributions should form the basis for a detailed dynamical understanding.

Molecular beam chemiluminescence from Na$\sb2$ + F $\to$ NaF + Na$\sp\*$ was dispersed and measured with a fast spectrograph. Attention was given to emission wavelengths at and around 388.5 and 342.8 nm, which correspond to the electric dipole forbidden atomic transitions Na 4s $\to$ 3s and 3d $\to$ 3s, respectively. It was hoped that the nascent products NaF and Na$\sp\*$ would interact such that these normally dis-allowed transitions could be observed, thereby constituting a direct glimpse of the three atom system late in the reaction event. A small emission peak was observed at the 3d $\to$ 3s transition wavelength, but its weak intensity could be explained by electric quadrupole radiation of the free atom rather than a reaction-induced breaking of dipole selection rules. No structured emission was observed at the 4s $\to$ 3s wavelength, although interference from Na$\sb2\sp\*$ may be obscuring an otherwise observable peak. In a second experiment, two lines of an argon ion laser are crossed with a single Na/NaCl beam in an effort to observe resolved laser-induced fluorescence of the stable molecule Na$\sb2$Cl. The copious emission from Na$\sb2\sp\*$ precluded any definitive identification of fluorescence from the target molecule. Finally, a detailed description is given of the f/2 spectrograph that was developed in this laboratory. The instrument observes a 100 nm wavelength region simultaneously, images atomic lines to a full-width-half-maximum (fwhm) of 2 nm, has a photocathode quantum efficiency of 3.1% at 800 nm, and exhibits only 36 counts per second dark current.

Photoelectron spectra of negatively charged iron, cobalt and nickel clusters in the size range of 5 to 20 (4 to 26) and 5 to 20 atoms respectively have been obtained. The electron affinity (E.A.) values along with the reported ionization potential (I.P.) have been used as a probe of the valence electronic structure of these clusters. This information is further used to understand the reactivity of the neutrally charged counterpart clusters of iron, cobalt and nickel with dihydrogen. An excellent anticorrelation between an empirically determined quantity called Ep, defined as IP $-$ EA $-$ e$\sp2$/r, and the reactivity of these clusters is observed. Ep is a direct measure of the polarizability of the clusters; The excellent anticorrelation is consistent with the Pauli Repulsion mechanism and is found to be a significant factor in controlling the reactivity of these clusters.

High resolution infrared diode laser kinetic spectroscopy has been used to investigate the properties of C$\sb2$H reaction kinetics. The ethynyl radical (C$\sb2$H) was produced in a flowing system by excimer laser photolysis (ArF, 193 nm) of either CF$\sb3$CCH or C$\sb2$H$\sb2$ and the transient infrared absorptions of C$\sb2$H or possible reaction products were followed with the diode laser probe. The kinetics of the C$\sb2$H + O$\sb2$ reaction were studied with a goal of determining the reaction products. Only two reaction products were observed, CO and CO$\sb2$, with the amount of CO produced being about five times larger than the amount of CO$\sb2$ produced. Both products are produced in vibrationally excited states. CO$\sb2$ was produced long after C$\sb2$H reacted and thus is not a product of the direct reaction. Two processes leading to CO formation have been observed: a fast, direct process for which the rate of CO appearance approximately matches the rate of C$\sb2$H decay and a much slower indirect process. The fast process produces vibrationally excited CO (v = 5 $\gets$ 4 and higher). The indirect process is observed to be dominant for the lower vibrational transitions and its rate exhibits saturation with increasing O$\sb2$ pressure. In order to approximate these kinetics, it appears that at least two intermediates between C$\sb2$H and CO must be involved for the indirect process. In other kinetic studies, the rate constants of C$\sb2$H reactions were measured to see if other C$\sb2$H reactions might exhibit addition channels. The time decay of a C$\sb2$H infrared absorption line originating from the ground vibronic state was monitored as a function of reactant pressure to determine a second order rate constant. When possible the dependence of the reaction rate on helium pressure was investigated over the range of 8-70 Torr. Second order rate constants of 3.0(2) $\times$ 10$\sp{-12}$, 1.3(3) $\times$ 10$\sp{-10}$, 3.6(2) $\times$ 10$\sp{-11}$, 4.4(4) $\times$ 10$\sp{-13}$, 2.3(3) $\times$ 10$\sp{-13}$ cm$\sp3$ molecule$\sp{-1}$ s$\sp{-1}$ were obtained for the reactions of C$\sb2$H with CH$\sb4$, C$\sb2$H$\sb4$, C$\sb2$H$\sb6$, H$\sb2$ and D$\sb2$ respectively. A third order rate constant of 2.1(3) $\times$ 10$\sp{-30}$ cm$\sp6$ molecule$\sp{-2}$ s$\sp{-1}$ was obtained for the reaction of C$\sb2$H with CO.

Symmetric-top molecules (CF$\sb3$Br, CF$\sb3$Cl, CF$\sb3$H and CH$\sb3$Br) in a seeded supersonic nozzle beam are orientation selected by a hexapole electric field, and collide at a right angle with fast (3-40 eV) potassium atoms. The ionization reactions at two different molecular orientations are studied: $$\eqalign{&\rm K + CX\sb3 - Y \to K\sp+ + CX\sb3 + Y\sp-\qquad (Tails\ Orientation)\cr &\rm K + Y - CX\sb3 \to K\sp+ + CX\sb3 + Y\sp-\qquad (Heads\ Orientation)\cr}$$ We observed that collision ionization reactions are influenced greatly by molecular orientations. For CF$\sb3$Br, CH$\sb3$Br and CF$\sb3$Cl, the reactivities are greater with the heads orientation than that with the tails orientation, but for CF$\sb3$H, the H end is unreactive. The steric effects are more pronounced at the low energy end near the thresholds, and almost disappear at energies above 20 eV. Most importantly, we also found that the energy thresholds of these reactions are different for heads and tails orientations, indicating that the electron affinity of a molecule should be considered as an anisotropic parameter. Some features of the experimental results are explained by the Harpoon Electron Transfer model. Further theoretical and experimental studies are required for the fully understanding of the reaction dynamics.

High resolution color center laser kinetic spectroscopy has been used to study the kinetics and spectroscopy of free radicals. The radicals are produced in a flowing system by the excimer laser photolysis of stable precursors. The transient infrared absorptions of the radicals are monitored with better than 1 $\mu$s time resolution. Spectra of the ethynyl radical (C$\sb2$H), produced by photolysis of acetylene, were collected between 3000 and 3600 cm$\sp{-1}$ with a goal of identifying the CH stretching fundamental of the molecule. A number of new bands of C$\sb2$H and its carbon-13 analogue ($\sp{13}$C$\sp{13}$CH) were observed and rotationally analyzed. These bands include three C$\sb2$H bands of $\sp2\Sigma\sp+$ + $\gets$ $\sp2\Sigma\sp+$ symmetry, one C$\sb2$H band of $\sp2\Pi$ $\gets$ $\sp2\Pi$ symmetry, three $\sp{13}$C$\sb2$H bands of $\sp2\Sigma\sp+$ + $\gets$ $\sp2\Sigma\sp+$ symmetry, and one $\sp{13}$C$\sb2$H band of $\sp2\Pi$ $\gets$ $\sp2\Pi$ symmetry. A number of $\sp{13}$C analogues of $\sp{12}$C$\sb2$H bands were identified. However, no conclusive assignment has been made for the CH stretch. Two tentative assignment schemes are given for several of the bands. The kinetics of the C$\sb2$H + O$\sb2$ reaction were studied with a goal of determining the reaction products. OH radicals were determined to be a minor product of this reaction. Experiments designed to determine the relative importance of the hydrogen atom producing channel were inconclusive. In other kinetic studies, a high temperature furnace was constructed to determine the temperature dependences of the product channels of the NH$\sb2$ + NO reaction. The reaction was initiated by the photolysis of NH$\sb3$ in the presence of NO. The branching ratios of the OH and H$\sb2$O producing channels were determined at 26, 400, 700, and 925$\sp\circ$C by comparison of the increase in OH and H$\sb2$O absorption signals with the decrease in an NH$\sb3$ absorption signal. Branching ratios were calculated from the raw signals by using the infrared cross sections of the molecules, measured in separate experiments. The branching ratio of the OH channel is 14% at room temperature and increases to 25% at 925$\sp\circ$C. The total of the two channels (OH plus H$\sb2$O) accounts for 100% of the reaction at room temperature; however, this number drops to about 80% for higher temperatures, possibly indicating the onset of another channel.

Synthesis techniques of carbon arc and laser vaporization in the furnace for production of fullerenes have been developed. The optimum conditions for the high yields of fullerenes were tested and studied. A fullerene growth model was proposed to explain the formation of the fullerenes and the extraordinary high yield of C$\sb{60}$. The results of a test of this growth model was in agreement with the implications of the model. The electronic spectra of neutral C$\sb{60}$ and C$\sb{70}$ in the regions from 375 to 415 nm and 595 to 640 nm have been studied in a supersonically cooled molecular beam by resonant two-photon ionization spectroscopy method. Sharp spectral features were observed in both regions for C$\sb{60}$ and in only the longer wavelength region for C$\sb{70}$. Neither molecule has the spectra that correspond to the diffuse interstellar bands. The first method to produce macroscopic quantities of internal metal-doped fullerenes was developed successfully and improved. Lanthanum-doped fullerenes were produced by laser vaporization of a lanthanum oxide/graphite composite rod in a flow of argon at 1200$\sp\circ$C. Many properties of these endohedral complexes were investigated in detail. Similar results were obtained with yttrium-doped fullerenes, and double-doped endohedral fullerene complexes were first observed as a stable species in both sublimed film and toluene solution. Macroscopic quantities of other interesting metal-doped or B-doped fullerenes have been obtained and studied. Purification of these metal-doped fullerenes is in the process.

A new apparatus capable of combining an external laser vaporization supersonic cluster beam source with a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer has been designed and implemented. Cluster ions generated in the supersonic beam source are injected down the bore of the superconducting ICR magnet and trapped in an elongated cylindrical FT-ICR ion trap. Cluster ions can be added into the ICR cell until it is filled to capacity, ensuring a high signal to noise ratio. Using standard FT-ICR techniques, specific cluster masses can be isolated with tailored excitation pulses, reacted with various reagent gases for times as long as several minutes, and examined with a mass resolution of over one million to one. This apparatus has been used to investigate the gas phase chemistry of silicon cluster ions. A systematic study of the silicon cluster reaction rate as a function of the cluster size has resulted in several remarkable results. Large fluctuations in reactivity are observed even for clusters as large as 50 atoms. Clusters containing 20, 21, 25, 33, 39, and 45 atoms are observed to be particularly inert. This result shows that these magic number clusters must have adapted a unique structure, or possibly set of structures, that exhibit a low reactivity towards ammonia. Kinetic analysis of the rate constants suggests that these unreactive clusters lack reaction sites capable of forming a strong silicon ammonia bond and/or lack sites capable of dissociatively chemisorbing ammonia. Comparisons of the cluster reactivity with the reactivity of various silicon surface reconstructions has lead to the development of an empirical model for systematically predicting the structure of silicon clusters starting at Si$\sb{20}$. This new model, based on filled pentagonal and hexagonal shell structures similar to the carbon Fullerene molecules and incorporating well established rules for silicon surface reconstructions, predicts covalently bonded clusters with $\pi$-bonded surfaces similar to the Si(111)(2 $\times$ 1) surface. The filled-Fullerene model successfully predicts the unreactive magic number clusters as being exceptionally stable structures in which all of the cluster surface dangling bonds participate in the surface reconstruction.